colon cancer meta. liver

I know that chemotherapy can cause the body to become toxic, necessitating the lowering of doses. Is it correct to assume though that lower doses will result in less efficacy? (potentially because the body becomes over exposed to it and stops responding?) Can small responses ultimately be as effective as dramatic improvements? And might the body recover from neuropathy such that Oxali might be resumed?

Also, at what levels are liver enzymes AST, ALT, and ALK PHOS levels dangerous/permanent?

Any information on any of these questions would be greatly appreciated.